Department of Biological Sciences, Florida Atlantic University, Boca Raton, FL 33431, USA.
Integr Comp Biol. 2023 Dec 29;63(6):1154-1167. doi: 10.1093/icb/icad111.
Shark skin is a composite of mineralized dermal denticles embedded in an internal collagen fiber network and is sexually dimorphic. Female shark skin is thicker, has greater denticle density and denticle overlap compared to male shark skin, and denticle morphology differs between sexes. The skin behaves with mechanical anisotropy, extending farther when tested along the longitudinal (anteroposterior) axis but increasing in stiffness along the hoop (dorsoventral or circumferential) axis. As a result, shark skin has been hypothesized to function as an exotendon. This study aims to quantify sex differences in the mechanical properties and morphology of shark skin. We tested skin from two immature male and two immature female sharks from three species (bonnethead shark, Sphyrna tiburo; bull shark, Carcharhinus leucas; silky shark, Carcharhinus falciformis) along two orientations (longitudinal and hoop) in uniaxial tension with an Instron E1000 at a 2 mm s-1 strain rate. We found that male shark skin was significantly tougher than female skin, although females had significantly greater skin thickness compared to males. We found skin in the hoop direction was significantly stiffer than the longitudinal direction across sexes and species, while skin in the longitudinal direction was significantly more extensible than in the hoop direction. We found that shark skin mechanical behavior was impacted by sex, species, and direction, and related to morphological features of the skin.
鲨鱼皮是一种由嵌入内部胶原纤维网络中的矿化真皮齿嵌入的复合材料，具有性别二态性。与雄性鲨鱼皮相比，雌性鲨鱼皮更厚，齿密度更大，齿重叠更多，而且雌雄鲨鱼的齿形态也不同。鲨鱼皮具有机械各向异性，沿纵向（前后）轴拉伸得更远，但沿环向（背腹或周向）轴拉伸时硬度增加。因此，有人假设鲨鱼皮的作用类似于外腱。本研究旨在量化鲨鱼皮的机械性能和形态的性别差异。我们沿着两个方向（纵向和环向），在 Instron E1000 上以 2 mm s-1 的应变速率进行单轴拉伸测试，测试了来自三个物种（锤头鲨 Sphyrna tiburo；牛鲨 Carcharhinus leucas；灰鲭鲨 Carcharhinus falciformis）的两个未成熟雄性和两个未成熟雌性鲨鱼的皮肤。我们发现雄性鲨鱼皮比雌性鲨鱼皮坚韧得多，尽管雌性鲨鱼皮的厚度明显大于雄性鲨鱼皮。我们发现，无论是在两性还是在各物种中，环向皮肤的硬度都明显大于纵向皮肤，而纵向皮肤的延展性明显大于环向皮肤。我们发现鲨鱼皮的机械性能受到性别、物种和方向的影响，并与皮肤的形态特征有关。
